1. Field of the Invention
The present invention relates to an automatic document feeder that makes it possible to scan both front and back faces of an original sheet of paper.
2. Description of the Related Art
As such a document feeder, there is an automatic document feeder (ADF) that automatically feeds an original sheet of paper to an original scanning section having at least a line sensor. Such an ADF is provided in a copier machine or a digital multifunctional peripheral including a scanner function and/or facsimile function as well as a copying function. Some of such copying machines or digital multifunctional peripherals include a function to scan both front and back faces of an original sheet of paper. A document feeder having one original scanning section needs to be devised in terms of transportation path or transportation unit to transport an original sheet of paper.
In one prior art, a guiding path, an inversion path and a delivery path are provided as a transporting path. When a front face of an original is scanned, the original is transported to a scanning position with transportation rollers of the guiding path and is sent out from the scanning position with transportation rollers of the inversion path. When a back face of an original is scanned, the original is transported with other transportation rollers of the inversion path and is sent out from the scanning position with transportation rollers of the delivery path. In this way, different transportation rollers are used when a front face or a back face of an original is scanned.
Further, instead of using different transportation rollers as described above, providing one transportation roller at one side of an image scanning section and rotating the transportation roller in normal and reverse directions, for example, allows the image scanning section to scan both faces of an original by switching the direction in which the original is transported. Furthermore, as another example, by using a triplet roller unit composed of a single drive roller and two driven rollers, both of which rotate in conjunction with the single drive roller, both faces of an original can be scanned by switching the direction in which the original is transported while the drive roller is rotating in one direction.